I am planning on starting to sell brewed tea at farmers markets. The main obstacles I see are :

1. Different teas have different brewing times, how to overcome this?
2. Re: point 1, if I brew the tea beforehand and sell from heated urns, I figure this greatly affect flavour. Or am I wrong? (the reason for this is, if it becomes busy it will become hectic if I have 10 or more orders and have to wait for brewing to finish.)
3. I am thinking only 4 basic teas (1 black, 1 green, 1 tisane, 1 "tea of the day"). What do you think of this?
4. Is there someone here that already does this?

Ciphrr wrote:
1. Different teas have different brewing times, how to overcome this?

You can’t.

Ciphrr wrote:
2. Re: point 1, if I brew the tea beforehand and sell from heated urns, I figure this greatly affect flavour. Or am I wrong? (the reason for this is, if it becomes busy it will become hectic if I have 10 or more orders and have to wait for brewing to finish.)

You will have to decide what kind of business you want to be, one that cares about tea and is hence slow. Or one that is efficient and neglects what a good cup of tea should be. There are business in Taiwan that sell bottled take-away tea, but brewed freshly in gong fu style. That takes time, so if there are lots of customers you have to wait. They just have lots of pots set up at the same time. Depending on your skills you can brew a few at the time.

Heated urns will let the tea continue to brew and oxidise. You can test how that affects the taste. Only some teas can take that treatment without tasting awful. None of them will taste good in the end. You can go Turkish with Samowar style brewing.

Masala chai is also an option. You can make it all at once in large quantities (I've never done it on the scale you're talking, but I know people that do), and the quality of tea is much less important than the choice of other ingredients and the skill of the brewer.